Hi,

The UI option "Edit As New Message" includes some headers from the
original message (e.g. References: ) that it shouldn't, and does so in
a way that is invisible to the user.

For example:

I posted to debian-private today as part of a thread, so my email had
a References: header in. A couple of people asked me to re-post on a
public list, so I sent to my Sent folder, selected "Edit As New
Message", edited the text a bit so it would make sense as a
stand-along post, and emailed it to debian-project.

You can see the result here:
https://lists.debian.org/debian-project/2018/12/msg00066.html

Note the References: header, which refers to posts in the
debian-private thread my previous email had been in reply to.

IMO, this violates the principle of least surprise - a "New Message"
in most senses would not contain such things; further it caused some
consternation among readers (who now find the -project and -private
threads get intermingled by their MUAs).

Thanks,

Matthew